1. Field of the Invention
The present invention relates to a solid state imaging device, particularly to amendment of deterioration of image quality that caused by false signals of a photoelectric conversion charge.
2. Description of the Prior Art
A solid state imaging device such as an interline type CCD image sensor or like that has a configuration composed of a photodiode 1, a CCD region 2, an isolation layer 3, a charge read-out region 4 and a neighbor CCD region 22 to the photodiode 1 as shown in FIG. 1A. In FIG. 1, FIG. 1A is a plane view of a pixel and FIG. 1B is a cross-section of FIG. 1A cut along X-Xxe2x80x2. In the solid state imaging device except for CCD, the region equivalent to the CCD region 2 is, though being not illustrated, a drain region of a transistor. Each of those solid state imaging device converts photo-signals coming in the photodiode 1 to electric charge signals by photoelectric conversion mechanism. These signal charges accumulated in the photodiode are read out by applied voltage to a transfer electrode (not illustrated) over an insulating film 9 in order to be taken out as electric signals.
When intense incident light comes to the solid state imaging device, an output image sometimes shows a color which does not originally exist in a photogenic object or thin vertical stripes. These phenomena came from false signals generated by that light rays which ought to come into a photodiode of a solid state imaging device. These rays are reflected or diffracted and converted to electric charge under the light shielding area, or the electric charge generated diffuses and comes in a neighboring photodiode and/or CCD region.
If such a diffusion charge comes in the neighboring photodiode across the isolation layer from the photodiode that covered by a color filter, it causes a false signal called xe2x80x9ccolor interferencexe2x80x9d and if such a diffusion charge comes in the CCD across the charge read-out region or an isolation layer, it causes a false signal called smear. Such false signals cause deterioration of the image quality.
The charge diffusion in a semiconductor is a common phenomenon caused by thermal effect even without electronic field. And the charge generated by photoelectric conversion has a long life until recombination since the electric charge is minority carriers in the isolation layer and a semiconductor region with the same conduction type as that of the isolation layer, the portion of electric charges reach a neighboring cell by diffusion during image pick-up duration.
Especially, the smaller the pixel size of the solid state imaging device is, the more serious the problem that caused by the false signal by the diffusion of photoelectric conversion charge in the isolation layer is.
An object of the present invention is therefore to provide a solid state imaging device capable of eliminating false signals caused by electric charge that is generated by photoelectric conversion and diffuses and comes in a neighboring photodiode and a CCD region.
In order to solve such a problem, inventors of the present invention provide a following solid state imaging device.
That is, a solid state imaging device of the present invention has a basic configuration comprising: a first conduction type semiconductor region, a plurality of photodiode diffusion layers with the first conduction type formed in the semiconductor region; opposite conduction type isolation layers formed shallower than a plurality of the photodiode diffusion layers in the semiconductor region and separating a plurality of the photodiode diffusion layers from one another; and trenches formed in the isolation layers and filled with an insulator material.
In the solid state imaging device with the basic structure of the present invention, a variety of embodiments are available for the trenches filled with the insulator material.
In the first practical embodiment, the trenches filled with the insulator material are formed in isolation layers which are located on the opposite to a charge read-out region neighboring the photodiode diffusion layer in relation to the photodiode diffusion layer.
In the second practical embodiment, the trenches filled with the insulator material are formed in isolation layers which are located between photodiode diffusion layers along charge transfer regions.
In the third practical embodiment, the trenches filled with an insulator material are formed in isolation layers which are located on the opposite to a charge read-out region neighboring the photodiode diffusion layer in relation to the photodiode and in isolation layers which are located between photodiode diffusion layers along charge transfer regions.
In the fourth practical embodiment, the trenches filled with an insulator material are formed at a plurality of positions at intervals from one another in the isolation layer in the solid state imaging device with the foregoing basic configuration and the solid state imaging device of the foregoing first, second, or third practical embodiment.
In the fifth practical embodiment, the trenches filled with the insulator material are formed as to have a continuous shape in the foregoing isolation layer in the solid state imaging device with the foregoing basic configuration and the solid state imaging device of the forgoing first, second, or third practical embodiment.
In the sixth practical embodiment, the photodiode diffusion layers in the solid state imaging device with the foregoing basic configuration and the solid state imaging devices of all of the forgoing practical embodiments have cap layers with opposite conduction type on the surfaces.